Indicator system for sacrificial anodes



June 5, 1962 L. F. VlXLER 3,037,920

INDICATOR SYSTEM FOR SACRIFICIAL ANODES Filed May 26, 1958 3Sheets-Sheet l FIG I v I 5l\ E 28 A 63 1 26 1 54 x 55 44 I 3 'L L g I 03J u N INVENTOR.

LESLIE F VIXLER ATTORNEYS June 5, 1962 F. VIXLER 3,037,920

INDICATOR SYSTEM FOR SACRIFICIAL ANODES Filed May 26, 1958 5Sheets-Sheet 2 1 M 73 76 i f MW u i! l INVENTOR.

LESLIE F VIXLER BY??? AQMMVJMM ATTORNEYS L. F. VIXLER 3,037,920-

INDICATOR SYSTEM FOR SACRIFICIAL ANODES v June 5, 1962 3 Sheets-Sheet 3Filed May 26, 1958 INVENTOR.

ATTORNEYS BYLESL/E F V/XLER FIG 8 FIG. 9

United States Patent Ofifice 3,037,920 Patented June 5, 1962 Ohio FiledMay 26, 1958, Ser. No. 737,572 5 Claims. (Cl. 204-148) This inventionrelates to hot water heater and storage tanks in which a so-calledsacrificial anode is employed to protect the interior surfaces of thetank from corrosion by galvanic action between the anode and the tank.The invention is directed to methods and apparatus for controlling thegalvanic action and for indicating the condition of the anode during itsactive life.

More particularly, the invention relates to new tank and anodeassemblies including an indicator for visually showing the galvanicactivity of an anode in the tank while the assembly is in use and,optionally, also including an additional electrical resistance elementin the metallic portion of the electrical circuit for limiting thegalvanic current flow, according to the conductivity of the water, to acurrent value no greater than that required to protect the tank frominternal corrosion. The invention also relates to special ammeters andtheir use in connection with the tank and anode assemblies and toimprove anode mounting structures particularly adapted for use where anammeter is included in the metallic portion of the electrical circuit.

In accordance with common practice, galvanic protection of the interiormetal surfaces of hot water heater and storage tanks may be accomplishedby mounting inside the tank, a metal element that is anodic, i.e., moreelectropositive or less noble, relative to the interior metal surface ofthe tank, and that is termed an anode or sacrificial anode. This anodeis electrically connected to the tank by a metallic circuit ofrelatively low electrical resistance, conventionally by a directmetallic connector by which the anode is suspended in the tank. When thetank is full of water, the anode is also electrically connected to theinterior surface of the tank through the water, which connectionprovides much greater resistance to the flow of electrical currenttherethrough than does the metallic circuit. Since the anode iselectropositive relative to the interior metal surface of the tank,galvanic electrical current is induced which may be considered asflowing around a closed circuit from the anode, through the water to theinterior surface of the tank, and through the low resistance etallicconnection from the tank back to the anode. The anode is slowly consumedby this galvanic action, whereas the interior metal surface of the tankis protected from corrosion thereby, the consumed metal of the anodeforming a reaction product with dissolved material in the water, whichreaction product generally is quite insoluble and is largely depositedon the walls of the tank to which the galvanic current flows.

Because the tank is protected at the expense of the anode, the anode iscommonly referred to as a sacrificial anode, as noted above. When theanode is entirely consumed as described, galvanic protection of the tankceases, and the anode must be replaced before this occurs if continuingprotection of the tank is to be maintained. However, the anode isnormally not visible, and its condition is normally determinable only byemptying the tank and removing the anode for inspection. This istroublesome and is often reglected, resulting in premature tank failuresfrom internal corrosion.

Depending upon the electrical conductivity of the water in the tank, thegalvanic current flowing through the anodetank circuit may be greaterthan needed to provide adequate tank protection, or it may be less thanneeded for 7 above.

this purpose. If the galvanic current is greater than needed, the rateof anode consumption is excessive, and some convenient means forreducing the current induced by a given tank and anode assembly isdesirable in order to prolong the life of the anode. If the galvaniccurrent is less than needed, the only remedy is to alter the anodearrangement so as to increase the anode surface area, as by using ananode having a larger surface or by using more than one anode to achievethe same effect.

Since the character of water supplies throughout the country varies overa considerable range, there has long been a need for a convenient way inwhich to control, at least to a susbtantial degree, the galvaniccurrents induced by waters of different conductivity. This is requiredin some instances to maintain a high enough current for adequate tankprotection, but is generally desired to prevent excessive current andrate of anode deterioration.

The use of a plurality of anodes has the advantage of enabling the anodesurfaces to be better distributed as regards their spacing from weldedjoints and other critical portions of the tank interior where corrosiontends to be concentrated, since the current flowing to various points onthe tank interior varies inversely with the length (resistance) of thewater path from those critical points on the tank surface to the nearestanode surface. This consideration makes it desirable in some cases,particularly in large diameter tanks, to employ a plurality of anodeseven though the resulting total galvanic current, and consequent rate ofanode consumption, becomes much greater than necessary. This accentuatesthe need for a convenient way in which to control the total galvaniccurrents induced in a given apparatus by waters of varying conductivity.

Particularly in the case of large and expensive, industrial water tanksdesigned to last for many years, when suitably protected, the aboveconsiderations make it important not only to limit the galvanic currentinduced so as to secure maximum anode life, but also to facilitatedetermining when anodes in the tanks have been consumed to the pointwhere they should be replaced. These problems have an important bearingon the ability of water tank manufacturers to guarantee the life oftheir product, since the life will depend upon the rate of anodedeterioration and the diligence of the customer in promptly replacingconsumed anodes. Also, the manufacturer normally has no way of knowinghow long a customers tank may have been neglected and retained in useafter the anodes have been consumed to the point where protection of thetank is inadequate. Thus, tank life guarantees have generally beenlimited to a period of time not greatly exceeding the expected effectivelife of the anode or anodes contained in a tank at the time of itsoriginal installation.

The objects of the present invention are to provide improved tank andanode assemblies which either eliminate or, at least, reduce each of theproblems discussed More specifically, the objects of the invention are:to provide convenient means for limiting the galvanic current so as topermit greater flexibility of tankanode designs for obtaining maximumtank protection without an excessive rate of anode consumption; toprovide simple and reliable means for indicating the condition of ananode or set of anodes in a tank while the tank is in use; and toprovide means associated with the electrical circuit of a tank-anodeassembly which will enable the tank manufacturer to determine whether ornot his customer has permitted the tank to remain in use after theprotective galvanic current (due to anode consumption) has dropped belowa safe value, whereby the manufacturer may safely offer longerguarantees of tank life conditioned upon proper maintenance of anodes byhis customers.

In accomplishing the foregoing objectives, greater tank life at minimumoriginal cost may be assured, accidental neglect causing premature tankfailures may be more easily avoided, and neglect as acause of prematuretank failures may be more readily detected.

' These objects and advantages of the invention are accomplished inaccordance with the inventionrby providing a resistor element in thegalvanic circuit having an electrical resistance selected to maintainthe proper galvanic current, the resistor elementpreferably beinginterchangeable with similar elements of different resistance values; byproviding an ammeter in the galvanic circuit which will continuouslyindicate the magnitude of the galvanic current and thereby show whenreplacement of anodes is required; and by providing a special ammeterfor the above purpose which, once the galvanic current has dropped belowa safe minimum on which a tank life guarantee may be based, will providethe manufacturer with knowledge of this fact and of the fact that thecustomers own neglect has voided the guarantee.

The foregoing objects, advantages, and features of the invention andpresently preferred embodiments thereof will be more fully understoodfrom the following detailed description of such embodiments of theinvention, and from the accompanying drawings in which:

FIGURE 1 is a vertical sectional view of a multiple anode Water heaterand storage tank assembly embodying the present invention, the sectionbeing taken as indicated by the line 11 in FIG. 2;

FIG. 2 is a horizontal sectional view of the assembly of FIG. 1, thesection being taken as indicated by the line 2-2 in FIG. 1;

FIG. 3 is a fragmentary, vertical sectional view of the assembly of FIG.1, on an enlarged scale, the section being taken as indicated by theline 3-3 in FIG. 2;

FIG. 4 is a fragmentary elevation on an enlarged scale of the assemblyof FIG. 1 taken as indicated by the line 44 in FIG. 3.

FIG. 5 is an enlarged, front, elevational view of an ammeter that ismounted in the assembly of FIGS. 1-3.

FIG. 6 is a side view of the ammeter of FIG. 4, taken as indicated bythe line 6-6 of FIG. 5 (but rotated 90 for convenience), with a portionof the ammeter case broken away to show certain interior structure, themounting panel for the ammeter also being shown in section in a positionto receive the ammeter and being shown in phantom outline with theammeter in position to be screwed to the panel, one of a pair ofmounting screws for this purpose also being shown.

FIG. 7 is a view similar to FIG. 6, but with the ammeter moved into itsmounted position in theaperture of the mounting panel.

FIG. 8 is a fragmentary, vertical sectional view,-on an enlarged scale,of the structure for mounting of the upper end of an anode on thetopwall of the tank in the assem bly of FIGS. 1-3, the plane of the sectionbeing taken as indicated by the line 88 in-FIG. 2;

FIG. 9 is a vertical sect-ion'alview of a modified em- 7 bodiment of theinvention in which a single anode is mounted in a water heater tank, thetank jacket and heating mechanism being omitted for simplicity; and

FIG; 10 is an enlarged fragmentary view, in vertical supported on threelegs 18 (only two being shown) be tween which a drip tray 19 may bemounted. A combustion zone 21 above the burner 17 is surrounded by alower are secured.

A collection zone 23 for combustion products is surrounded by an upperextension 24 of the tank side wall. The top wall 14 of the tank formsthe bottom of the collection zone, and an apertured plate 26 forms thetop wall of the collection zone. Hot, gaseous, combustion products fromthe burner 17 pam from the combustion zone 21, upwardly through fourheader conduits 27, and into the collection zone 23, from where theypass out of the apparatus through a flue pipe 28 communicating with thecentral aperture of the plate 26.

Inside the tank 10 are mounted three sacrificial anodes 30 of identicaldesign. Each anode 30 is preferably a rod of magnesium alloy for use ina lined or unlined tank It} of steel, galvanized steel, aluminum, orother metal or alloy to which the magnesium alloy is anodic. Referrin gto FIG. 8, as well as to FIGJI, each magnesium anode 30 is preferablyformed around a core wire 31 which extends from top to bottom throughthe magnesium alloy rod in surface-to-surface electrical contacttherewith.

The core wire should be of a metal that is more noble than the metal ofthe anode. It may suitably be steel or aluminum, for example.

The upper end 32 of each anode is of reduced diameter and is externallythreaded, leaving an annular shoulder 33 for engagement by an annularwasher 34 of electrically insulating material surrounding the upper end32 of the anode. The threaded upper end 32 of the anode is screwed intoan internally threaded insulating sleeve 36 molded and retained by aflange 37 in the bore of a fitting 38 having an enlarged head 39 shapedto be turned by a wrench. The thickness of the sleeve 36 is sufficientto leave a substantial clearance space 35 between the flange 37 and theanode.

The cap 38 is screwed onto the anode until the flange 36 thereof engagesand compresses the washer 34 to provide a watertight seal and therebysupport the anode insulated therefrom by the washer 34, air space 35,and sleeve 36. The cap 38, which may be provided with a sealing washer40, if desired, is externally threaded and screwed into an internallythreaded ring 41 projecting snugly through an aperture in the top wall14 of the tank and having an outer flange 42 engaging the top wall ofthe tank about the aperture therethrough. A watertight joint between thering 41 and the top wall of the tank is provided by an external and aninternal peripheral weld as indicated in FIG. 8.

As will be apparent, the cap 38', with an anode 30 threaded therein, maybe mounted as described and removed for replacement of the anode whenneeded. Also, the anode may thus be suspended by its upper end from thetop wall 14 of the tank while being electrically insulated therefrom.Each anode 39 is mounted as described.

Electrical contact between the anodes 30 and the tank 10, of course, ismaintained by the water in the tank, which constitutes an electrolytenormally having a relatively high resistance. The galvanic currentflowing from the anodes to the tank through the water in the tank iscarried by a low resistance conductor 44 (FIG. 3) con necting a tankcontact 46 to one terminal of an ammeter 47 mounted externally of thetank 10. The current flowing through the ammeter 47 is then carried by asecond low resistance conductor 48 from a secondterminal of the ammeterto a low resistanceconnector plug 49 (suitably made of brass andinsulated from the tank 10 as V hereinafter described), and thencethrough the plug 49 to the inside of the tank, at which point thecurrent is divided 'betwen three parallel, low resistance conductors 50that respectively connect the plug 49 to the core wire 31 at the lowerends of the three anodes 3%. Thus, a closed metallic circuit is providedfor the galvanic current from the anodes 30 through the water in thetank to the tank itself, from the tank through the ammeter 47,

and back to the anodes through the plug 49. As a result, the ammeter 47constantly registers the total galvanic current from the three anodes 30to the tank 10.

The conductor 44 from the tank to the ammeter 47 may be permanentlysoldered at one end to its ammeter terminal and be soldered at itsopposite end to a pushin connector or the like adapted to be removablysnapped into a socket in the tank contact. The conductor 48 from theammeter may be permanently soldered at one end to its ammeter terminaland be soldered at its opposite end to a push-in connector or the likeadapted to be removably snapped into the plug 49. The three conductors50 from the plug 49 to the anodes 30 may be permanently soldered to thelower ends of the three anodes, respectively. The opposite ends of theseconductors may have push-in connectors or the like soldered thereto andadapted to be removably snapped into sockets in the inner end of theplug 49.

Access to the interior of the shell 11 and to the interior of the tank10, for purposes of initial assembly of the electrical circuit and forservice incident to the replacement of anodes, may be provided throughaccess openings that are normally closed by a shell closure plate 51 anda tank closure plate 61. The shell closure plate 51 is preferably alsoused as a mounting panel for the ammeter 47 and may be secured in placeby a plurality of rigid hooks and spring clips. The rigid hooks mayinclude two or more S shaped members 52 (only one being shown)distributed along and welded to the inner surface of the closure plate51 and hooked over the lower edge of the opening in the shell 11. Thespring clips preferably include two clips 53 spaced apart a few inchesalong, and welded to, the inner surface of the closure plate 51, asshown in FIG. 4. The clips 53 may be of a cam actuated type which willbe cammed downwardly when pressed inwardly against the upper edge of theopening in the shell 11, and which will then snap back to lock theclosure plate firmly in place, as shown in FIG. 3, so as to resistprying this closure plate off from the outside. To remove this closureplate, it will then be necessary first to remove the a'mmeter 47 byremoving its mounting screws 54, the purpose of this being explainedhereinafter. Then one may reach through the opening in the closure plate51 and forcibly pull the clips 53 downwardly against their springaction, while also pulling outwardly on the upper portion of the closureplate 51, to tilt the plate outwardly until the clips 53 are disengaged.Thereupon the closure plate can be lifted upwardly and outwardly todisengage the hooks 52 and free the closure plate for removal. Athickening and stiffening bar 55 may be welded along the upper edge ofthe access opening in the shell 11 if desired.

The tank closure plate 61 may be removably mounted on a flange 62 aboutthe tank access opening by a suitable number of bolts 63 (two beingshown), with an electrically insulating gasket plate 64 disposed betweenthe closure plate and the mounting flange and covering the inner surfaceof the closure plate.

The plug 49 is mounted in the tank closure plate 61 and is electricallyinsulated therefrom. As shown in FIG. 3, an opening through this closureplate may be lined with an electrically insulating gasket sleeve 66. Ifdesired, the gaskets 64 and 66 may be integral and be molded onto theclosure plate. The plug 49' may be externally threaded and have an outerhead adapted to overlie and seal against an outer flange on the gasketsleeve 66, and it may be secured in place by an internal nut overlyingand sealing against the gasket plate 64. In this manner water leakagearound the plug 49 may be reliably prevented while also electricallyinsulating the plug 49 from the closure plate 61 and from the tank 10.Also, initial assembly and disassembly for servicing may readily beaccomplished in an obvious manner.

In order to limit the galvanic current to a suitable value for adequatetank protection, it may be desirable to increase the resistance of themetallic conductor portion of the closed galvanic current circuit. Thismay readily be done by using an ammeter having a high enough internalresistance for this purpose. Alternatively, additional resistance may beinserted at any desired point in this part of the circuit in series withthe ammeter.

The ammeter 47, for the purposes of the present invention, preferablyhas a non-linear response to variations in current where a needle typeindicator is used. For example, the lower third of the scale (designatedA in FIG. 5) may cover the range from O to only 20 milliamperes and theupper two-thirds of the scale (divided into parts designated B and C inFIG. 5) may cover the range from 20 to 120 milliamperes. For a tank andanode arrangement of the type illustrated in FIGS. 1-3, having, forexample, about 55 square feet of exposed galvanized steel tank surface,the maximum galvanic current may be limited by the resistance of thecircuit to about milliamperes (corresponding to about 2.0 milliamperesper square foot of tank surface), and the desirable minimum current maybe about 55 milliamperes (corresponding to about 1 ma./ sq. ft. of tanksurface). This range may be that represented by the segment C of thescale in FIG. -5 and be the desired operating range. The segment B maycover a range down to about 20 milliamperes (corresponding to about 0.4ma./sq. ft. of tank surface) representing a danger point below which thecurrent must not be permitted to drop. It is contemplated that this maybe made a condition in the manufacturers warranty. The range representedby the segment A of the scale in FIG. 5 will then drop from 20milliamperes to zero.

Accordingly, an ammeter reading dropping into the range of zone A is anoccurrence which the manufacturer will wish to be informed of so that hewill know that he has been relieved of responsibility under his warrantyby the neglect of the customer. To this end, the ammeter 47 is providedwith means for blocking movement of an indicator needle 70 in eitherdirection past the division line between segments A and B of the scaleon the ammeter dial or face 71 when the ammeter has been demounted fromits mounting panel. This means may comprise an elongated leaf spring 72having one end welded or otherwise secured against the back side of amounting flange 73 of the ammeter case, as best shown in FIG. 6. Asshown, the spring is normally biased to extend at an angle away from theback side of the flange 73 on which it is mounted, and to extendinwardly into the ammeter case 74 through an aperture 75. The oppositeend of the spring 72 may have a small diameter wire 76 soldered theretoand extending transversely therefrom through a small aperture 77 in theammeter dial or face 71. The wire 76 may project in a straight linethrough the ammeter dial 71 and beyond the plane in which the needle 70swings; then be bent approximately through a right angle so as to extendgenerally parallel to the dial 71 to a point directly opposite thedivision line on the dial between segments A and B of the ammeter scale;-and then be bent again approximately through a right angle to provide afree end portion extending toward the dial and into the path of theneedle 70 at the division line between scale segments A and B.

As will be apparent from the foregoing, the free end portion of the wire76, when the ammeter is demounted, will provide an obstruction tomovement of the needle 70 in either direction past the division linebetween scale segments A and B. However, when the ammeter is mounted onits mounting panel 51, as shown in FIG. 7, the panel engages the leafspring 72, depresses it against the flange 73 of the ammeter case, andmoves the wire 76 to shift its free end portion out of the path of theneedle 70. When the ammeter is demounted again, the

wire 76 will again move into the path of the needle 70. Thus, the needleobstructing mechanism just described will hold the needle 70 on eitherthe high or low side of the division line between scale segments A and Bwhen the arnsmeter is demounted, according to where the needle was atthe time of demount-ing.

The method of utilizing the described needle-blocking mechanism is asfollows: The customer using the water heater and storage tank may beinstructed that anodes must be replaced when the needle 70 of theammeter has moved from scale zone C into scale zone B and before itreaches scale zone A on the ammeter dial. The instructions for replacinganodes may specify that the first step in replacing anodes afterdraining the tank 11) is to demount the ammeter 47 While it is stillelectrically connected in the anode circuit. This releases the leafspring 72 and traps the needle on the high or low side of the divisionline between-scale segments A and B. The instructions may specify, asthe next steps, that the conductors 44 and 48 be disconnected from thetank and from the plug 49 so as to free the ammeter for return to themanufacturer for inspection, the closure plate 61 be removed, the anodewires 50- be disconnected from the plug 49, and the anodes 30 be removedfrom the tank for replacement. The manufacturers warranty of the tank 10may be conditioned upon timely replacement of anodes and upon compliancewith his service instructions.

By mounting the ammeter 47 on the shell closure plate 51 and locking theshell closure plate onto the shell as shown in the drawing and describedabove, the prescribed order of steps can be reasonably assured. Theammeter must be removed before the closure plate 51 can be removed oranything done to break the anode circuit, thus trapping the ammeterneedle and showing whether or not the galvanic current had first droppedbelow the critical danger point. By also requiring return of the ammeteras a condition to the purchase of replacement anodes, the manufacturercan be reasonably sure that he receives a correct indication of whetheror not the customer broke a condition of the manufacturers warranty bydelaying too long before replacing the old anodes. With this protection,the tank manufacturer may advantageously guarantee a longer life for histanks and educate his customers to use care in the maintenance of thetanks, with consequent advantages to both.

FIGS. 9 and 10 illustrate a modified embodiment of the invention whichis particularly suitable for relatively small tanks in which a singleanode provides sufficient tank protection. For simplicity, no outer tankshell or burner, etc., have been shown, and the connection of an ammeterA into the anode circuit has been shown somewhat diagrammatically. It isto be understood, however, that the ammeter should be suitably mountedand connected as a part of the complete assembly, as in FIGS. 1-3', byutilizing any suitable ammeter mounting structure.

1 Preferably, the ammeter A is provided with a mechanism for holding orblocking the ammeter indicator, such as that illustrated in FIGS. 7, forholding the indicator on one side or the other of a scale pointseparating a safe current range from an unsafe one. The principalpurpose of FIGS. 9 and is to illustrate a modified construction forsupporting an anode and'connecting it electrically to the ammeterwithout running conductor wires inside the tank. a a i 'As shown inFIGS. 9 and 10, a tank 80 may have an inwardly directed flange 81 aboutan opening through the top wall thereof, and an anode-supporting fitting82 may be removably threaded into the flange 81 with an anode 84depending from the fitting. The connection between the anode 84 andfitting 82 is shown in vertical section in FIG. 10. 9

Referring to FIG. 10, the fitting 82 may have a longitudinal bore oflarge diameter over its lower portion with an inwardly directed,annular, sleeve-retaining flange 86 about the lower end of this bore. Anelectrically insulating and sealing sleeve 87 is formed in this bore, asby molding it therein, the sleeve being substantially thicker than theretaining flange 86 and being internally threaded. A reduced diameterupper end portion 88 of the anode 84 is externally threaded and providesa shoulder 39 for seating an electrically insulating and sealing washer91. The upper end portion 88 of the anode is screwed into the sleeve 87so as to be supported thereby in physically spaced relationship with thefitting 82, while compressing the washer 91 between the shoulder 89 ofthe anode and the sleeve-retaining flange 86 of the fitting. Thus, theanode is insulated from the fitting 82 and from the tank 89 and leakagearound the anode is prevented by two electrically insulating seals madeby the sleeve 87 and the washer 91.

The upper portion of the fitting 82 may have a bore of smaller diametertherethrough and be internally threaded to receive a plug 92. The lowerend portion of the plug 92 may have a hollow bore lined with an elasticinsulating sleeve 93. A metal sleeve 94 is forced into the elasticsleeve 93 to compress it radially and hold both of the sleeves 93 and 94in place in the plug 92. The central portion of the plug 92 may have ahollow bore of slightly reduced diameter for receiving a resistor 96 ofappropriate electrical resistance. The upper end portion of the plug 92may have a still smaller bore therethrough for an insulated electricalconductor 97 that is connected to one terminal of the resistor 96 andpasses out of the upper end of the plug 92. The opposite end of theresistor 96 is connected to an electrical conductor 98 that projectsthrough and slightly beyond the lower end of the metal sleeve 94 and issoldered thereto by a button of solder 99 constituting a second terminalfor the resistor that is electrically insulated from the plug 92 by theinsulating sleeve 93.

In this case, a core wire 101 in the anode 84 preferably projectsupwardly a short distance beyond the upper end of the anode forpositioning a helical spring 102, of low electrical resistance, inspaced relationship with the inner walls of the metal fitting 82. Afterthe anode is threaded into the lower end of the fitting 82, the spring102 is dropped into place through the upper end of the fitting, and theplug 92 is then threaded into the upper end thereof to compress thespring between the end of the anode and the solder button 99. v

The resistor 96 is preassembled in the plug 92 by inserting it into thelower end of the plug with its conductors 97 and 98 attached, and theninserting the insulating sleeve 93 and metal sleeve 94. Thereupon thesolder button 99 is applied to complete this preassembled unit. Ifdesired, the upper end'of this assembly may be closed about theconductor 97 by filling the cavity in the plug 92 above the resistor 96with a sealing wax or the like (not shown). Such preassembled units maybe made and stocked with diifer'ent resistors mounted therein, unitshaving the proper resistance being selected for installation to limitthe maximum galvanic current as required by waters of differentelectrical conductivity. Where the resistance of the ammeter A is highenough for this purpose, the resistance of the resistor 96 may desirablybe virtually zero, and the resistor may function strictly as aconductor; or the resistor 96 and conductor 98 may be eliminated and theconductor 97 connected directly to the solder button 99.

Thus, the insulated conductor 97 is connected through an easilyreplaceable resistor 96 to the anode 84. By connecting the conductor 97to one terminal of the ammeter A, and by connecting the other terminalof the ammeter through a conductor 103 to any suitable electricalcontact on a wall of the tank 80, a galvanic circuit is completed withthe metallic connections of the ammeter to the tank and to the anodebeing entirely accessible from outside the tank and sealed from directcontact with the water in the tank. a I

As will be apparent, the anode mounting structure of FIGS. 9 and 10 maybe used in multiple anode tanks, if desired, and is particularly usefulin any installation where it is considered advantageous to dispense withan access opening into the tank. Similarly, of course, the generalarrangement of FIGS. 1-8 may be used for a single anode installation, aswell as for a multiple anode installation utilizing any desired numberof anodes.

From the foregoing description of illustrative embodiments of thepresent invention, it will be apparent that simple and effective meanshave been provided for achieving the various objects and advantages ofthe invention. It will also be apparent that many equivalents of thespecific structures disclosed may be employed while utilizing theessential features and principles of the invention. Accordingly, theinvention is intended to include all such equivalents.

Having described my invention. I claim:

1. A method of aflording a continuous galvanic protection to theinterior surfaces of a metal water storage tank during use of said tankcomprising the steps of mounting within a metal water storage tank asacrificial metal anode that is anodic with respect to the metal of theinterior of said tank, mounting on said tank an ammeter having a currentresponsive indicator movable along a path of travel in proportion to thecurrent passing through the ammeter over the current range to which theammeter is responsive, electrically connecting said ammeter in seriesrelation between said tank and said anode so that movement of saidindicator along its path of travel will indicate the progressive stagesof decomposition of said anode, providing said ammeter with stop meansoperative when said ammeter is demounted from said tank to hold saidindicator against movement past a location along its path of travelcorresponding to a predetermined minimum galvanic current, anddemounting said ammeter from said tank to render said step meansoperative before electrically disconnecting it for replacement of saidanode.

2. A method of affording galvanic protection of the interior surfaces ofa metal water storage tank during the use of said tank comprising thesteps of mounting within a metal water storage tank a sacrificial metalanode that is anodic with respect to the metal of the interior of saidtank, detachably mounting on the exterior of said tank an ammeter havingan indicator movable along a path of travel in proportion to the currentpassing through the ammeter over the current range to which the ammeteris normally responsive, electrically connecting said ammeter inseriesrelation between said tank and said anode so that movement of saidindicator along its path of travel will indicate progressive stages ofdecomposition of said anode, blocking movement of said indicator ineither direction past a predetermined location in its path of travelwhen demounting said ammeter from said tank, electrically disconnectingsaid ammeter, and replacing said anode.

3. In a water storage tank assembly comprising a metal water storagetank and a sacrificial metal anode within the tank that is anodic withrespect to the metal of the interior of the tank, the combinationtherewith of: means mounting the anode on the wall of the tank, saidmounting means including means electrically insulating the anode fromthe tank, an ammeter mounted on the exterior of the tank and including acurrent responsive indicator mounted for movement along a path of travelin proportion to the current passing through the ammeter over a currentrange to which the ammeter is normally responsive, conductorselectrically connecting the ammeter in series between the tank and theanode, and means mounted on the ammeter and operative when the ammeteris demounted from the tank for restraining movement of said indicatorpast a point corresponding to a predetermined minimum galvanic current.

4. In a water storage tank assembly comprising a metal water storagetank and a sacrificial anode within the tank that is anodic with respectto the metal of the interior of the tank, the combination therewith of:means mounting the anode on a wall of the tank, said mounting meansincluding means electrically insulating the anode from the tank, anammeter mounted on the exterior of the tank and including a currentresponsive indicator mounted for movement along a path of travel inproportion to the current passing through the ammeter over the currentrange to which the ammeter is normally responsive, electrical conductorsconnecting the ammeter in series between the tank and the anode, andmeans mounted on the ammeter for movement into the path of travel ofsaid indicator at a predetermined location in said path in response todemounting the ammeter from said tank for blocking movement of theindicator past said location in either direction.

5. In a water storage tank assembly comprising a metal water storagetank and a sacrificial metal anode within the tank that is anodic withrespect to the metal of the interior of the tank, the combinationtherewith of: means mounting the anode on the wall of the tank, saidmounting means including means electrically insulating the anode fromthe tank, an ammeter mounted on the exterior of the tank and including acurrent-responsive indicator mounted for movement along a path of travelin proportion to the current passing through the ammeter over thecurrent range to which the ammeter is normally respon sive, electricalconductors connecting the ammeter in series between the tank and theanode and stop means mounted on the ammeter for normally blockingmovement of said indicator past a predetermined location along its pathof travel in either direction, said stop means including meansresponsive to mounting engagement of said ammeter with said tank forrendering said stop means inoperative.

References Cited in the file of this patent UNITED STATES PATENTS2,150,836 Lamb Mar. 14, 1939 2,308,687 Harrison Jan. 19, 1943 2,486,871Osterheld Nov. 1, 1949 2,508,171 Kaufman May 16, 1950 2,568,594 RobinsonSept. 18, 1951 2,656,314 Osterheld Oct. 20, 1953 FOREIGN PATENTS 412,322Canada May 4, 1943

1. A METHOD OF AFFORDING A CONTINUOUS GALVANIC PROTECTION TO THEINTERIOR SURFACES OF A METAL WATER STORAGE TANK DURING USE OF SAID TANKCOMPRISING THE STEPS OF MOUNTING WITHIN A METAL WATER STORAGE TANK ASACRIFICIAL METAL ANODE THAT IS ANODIC WITH RESPECT TO THE METAL OF THEINTERIOR OF SAID TANK, MOUNTING ON SAID TANK AN AMMETER HAVING A CURRENTRESPONSIVE INDICATOR MOVABLE ALONG A PATH OF TRAVEL IN PROPORTION TO THECURRENT PASSING THROUGH THE AMMETER OVER THE CURRENT RANGE TO WHICH THEAMMETER IS RESPONSIVE, ELECTRICALLY CONNECTING SAID AMMETER IN SERIESRELATION BETWEEN SAID TANK AND SAID ANODE SO THAT MOVEMENT OF SAIDINDICATOR ALONG ITS PATH OF TRAVEL WILL INDICATE THE PROGRESSIVE STAGESOF DECOMPOSITION OF SAID ANODE, PROVIDING SAID AMMETER WITH STOP MEANSOPERATIVE WHEN SAID AMMETER IS DEMOUNTED FROM SAID TANK TO HOLD SAIDINDICATOR AGAINST MOVEMENT PAST A LOCATION ALONG ITS PATH OF TRAVELCORRESPONDING TO A PREDETERMINED MINIMUM GALVANIC CURRENT, ANDDEMOUNTING SAID AMMETER FROM SAID TANK TO RENDER SAID STOP MEANSOPERATIVE BEFORE ELECTRICALLY DISCONNECTING IT FOR REPLACEMENT OF SAIDANODE.